1. Field of the Invention
The present invention relates to the preparation of prepolymers composed of either or both of polyimide and polybenzimidazole as organic precursors for producing monolithic porous carbon disks with density less than or equal to 1.0 g/cc; and the processes for producing monolithic porous carbon disks from either or both of polyimide and polybenzimidazole procurers in the form of powders. The present invention further relates to the processes for producing monolithic porous carbon disks derived from either or both of polyimide and polybenzimidazole precursors having one or more than one metals dispersed therein. The present invention even further relates to the processes for producing monolithic porous carbon disks derived from either or both of polyimide and polybenzimidazole precursors such that the carbon disks having pyridine-like structure wherein the transition metal atoms are caged in or complex with.
2. Description of Related Art
Monolithic porous carbon disks, which possess interpenetrating pore structure, high density, high surface area, suitable pore size, and well defined pore size distribution, are highly desirable as electrode materials for lithium batteries, electrochemical capacitors, fuel cells, as well as other electrochemical devices.
One approach to produce monolithic porous carbon disk is through sol-gel technologies. The sol-gel technology generally consists of preparation of gels from solution, drying the gel while minimizing the gel shrinkage. The pyrolysis of thin gel films yields porous monolithic carbon disks. RF carbon aerogel currently in the market as electrode material for supercapacitors is derived from resorcinol and formaldehyde organic precursors. RF carbon aerogel provide high surface area and narrow pore size distribution. Yet, the potential market of RF carbon aerogel as electrode material for ultracapacitors is severely limited by the low operating voltage of the capacitor (<=5V) and high manufacturing cost of monolithic RF carbon aerogel materials.
Another approach to produce monolithic porous carbon disks is from powders of porous polymeric precursors by compressing them into monolithic disks followed by pyrolysis. There are two (2) obstacles in this approach. One is the compressibility of the polymer precursor and other is the difficulty in retaining interpenetrating network of the pores during the compression process. U.S. Pat. No. 6,544,648 discloses a process for making monolithic carbon disks by compressing carbon black powder with high surface area under vacuum environment at temperatures at or beyond 800° C. and a pressure at or beyond 3000 psi. This approach produces carbon disks with more undesirable micro-pores with pore diameter less than 2 nm than the ones by sol-gel approach. The compression of carbon powder under vacuum at 800° C. displays sever technical challenges and high manufacturing costs.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide monolithic porous carbon disks with high surface area, high pore volume, high surface activity, well defined pore structure and morphology, and good mechanical properties. It would also be desirable to provide a process for producing such monolithic porous carbon disks with significantly lower cost as compared to the processes currently in the market.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.